Monday, January 14, 2008

Hibernate, Encapsulation and OO

The current project I am working on, is a typical legacy application rewrite. The existing system in cobol has been around for ages and the code base had apparently got very bloated and unstructured with so many patches/fixes/what-not down the years.

One of the main issues in the old system was that the code had become un-manageable and making a small change involved poring over thousands of lines of code to find out where something was getting changed.

In the proposed java based system, in the tradition of all enterprise applications, we would be using hibernate and spring. When we reverse engineer Hibernate/JPA entities from DB schemas the java objects created have public getter/setters. This seemingly innocuous feature is the one I have a biggest gripe with. This totally violates the whole data abstraction notion in OO systems.

When the entities are exposed as such, it becomes easy for layers above it to change entity state. This is very convenient when writing code and lets one design classes that updates multiple entities. But this also leads into the same problem which caused the rewrite in the first place. By letting anyone update entities, we allow business logic to be just dumped into a class and be called. No structure is need.

I prefer having one gateway class where all business logic pertaining to one entity is located. This simplifies making any changes to the system and any impact analysis need not span the entire code base. But in a model where entities have public setters, this can never be enforced.

Whats to prevent the current rewrite from being as messed up as the system its replacing? Processes like code review helps to a certain extent. But when push comes to shove, cutting corners becomes the norm and out goes all the best practices. This leads us back into creating our own tangled web of code to replace the older tangled web. It may seem too far-fetched but after 8 years of looking/writing all sorts of patches/fixes and features, only one thing is certain. If it can be abused, it eventually will end up being. Maybe even by the original developers ;)

ObjectMentor has a blog posting about this that states that jpa/hibernate entities should be treated as datastructures and not objects. They suggest adding a new layer of objects that map to the hibernate/jpa data structures and the rest of the application code uses the created objects.

This is a good idea in that we can create proper OO code that are not limited by the active record style entity objects. This can potentially even help in resolving some of the issues i had with anemic data model.

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1 comment:

Eliot Sykes said...

Would you be willing to take some time to provide an example to show a way on how to use Objects and Active Records together in the way you and ObjectMentor suggests? I’m having trouble working out what an implementation might look like.

Kindest regards,


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